A. Field of the Invention
The present invention is related to water cooled panels for electric arc furnaces and more particularly to a water cooled panel having a tubular design comprised by a coil formed by a thick wall pipe in which the 90° & 180° elbows are integral to the tube, and to its forming method.
B. Description of the Related Invention
Temperatures higher than 2300° F. are generated inside the electric arc furnaces, therefore, in order to avoid structural damages, water cooled panels are used in order to maintain the temperature of the structure below the failing point.
Typically, an electric arc furnace has several cooling systems. Normally, those systems comprise a cooling liquid recirculation circuit passing through all the elements of the furnace exposed to high temperatures. The water circulating inside the circuits, passes through the elements that need to be cooled such as Shell & Roof panels, gas exhaust Ducts, etc., in order to remove heat from those elements and subsequently transfer that heat to the environment using a cooling tower or an equivalent device.
The cooling circuit is typically comprised by several feeding pumps, return pumps, filters, one or more cooling towers as well as supervision and control instruments. The key elements of the furnace normally have instruments to monitor the flow, pressure and temperature of the water.
For most water cooled equipment, a flow interruption or an inadequate volume of water circulating through the cooling system may cause a serious thermal overload and sometimes a catastrophic failure.
Current electric arc furnaces have a variable quantity of water cooled panels mounted on a support frame, which allows for quick individual replacement of each panel. By cooling the furnace structure, thermal expansion and thermal stress are avoided which may cause gaps between panels. Water cooled panels allow the furnace to withstand high temperatures without suffering any structural damage. In old design electric arc furnaces, such high temperatures may have caused a higher erosion rate of the refractory walls and damages to the furnace shell.
Furthermore, cooling coils are used in the gas exhaust Ducts in order to cool said Ducts and avoid a structural damage and to cool down the gases to an adequate temperature for the filters to which the gases are conducted.
Typically the water cooled panels have a tubular design and comprise a hydraulic circuit requiring more than one pipe. In order to conduct the water from one pipe to the next one in the circuit, 90° & 180° elbows are used. This kind of hydraulic circuit is normally called “coil”.
The use of said 180° elbows allows for a gap between the pipes that ranges from 0 to approximately a distance equivalent to the diameter of the pipe. Said 180° elbows are formed (cast, forged) independently of the pipes and are welded to the end of each pipe.
The process of welding an elbow to the ends of the pipes is costly, time consuming and creates a potential failure point.
Furthermore, the internal welded seams may cause additional pressure losses when the coil is in operation, reducing the eficiency of the entire cooling system.
Based on the above referred problems, the applicant developed a novel pipe bending method, comprising a simultaneous hot bending and pressing of the pipe by which it makes possible to obtain a coil without welded 180° elbows since they are integrally formed with the pipe.
By using the above referred novel process it is possible to bend a thick wall pipe to obtain a 180° elbow, with a gap between straight pipe sections which can go down to zero inches.
The method of the present invention may be applied to pipes made of carbon steel, copper (and its alloys), stainless steel, low alloy steel, aluminum, etc. in order to produce tubular cooling coils for electric arc furnaces elements such as shell & roof panels, tunnels, slag doors, sump panels, deltas, rings, ducts, drop out boxes, post-combustions chambers, etc.
The water pressure losses obtained with the novel method are equal or lower than the pressure losses obtained with the coils having welded elbows, thus optimizing the amount of electric energy used by the pumps which circulate the water through the cooling system.